To compute sine or cosine often requires argument reduction that can be a significant portion of the running time of the method. If both sine and cosine of the same value are needed, this argument reduction is unnecessarily repeated.

A sincos(x) methods that return a the pair of sine and cosine values would allow the argument reduction to be reused.

See thread https://mail.openjdk.org/pipermail/core-libs-dev/2026-January/158433.html